This application is based on and incorporates herein by reference Japanese Patent application No. 2001-22103 filed on Jan. 30, 2001 and Japanese Patent Application No. 2001-354598 filed on Nov. 20, 2001.
1. Field of the Invention
The present invention relates to a method for vibrating, melting and bonding a plurality of resin parts in which the contact surfaces of resin parts are vibrated, to cause melting and subsequent bonding of the parts.
2. Description of the Related Art
In the background arts, there is a low cost vibrating, melting and bonding method as a method for bonding resin parts to each other. This method is performed as follows. First, while a plurality of resin parts are pressed onto each other, they are made to abut against each other and their contact surfaces are vibrated to melt the resin at the contact surfaces by the use of frictional heat generated by the vibration. Then, when the resin at the contact surfaces is melted, the vibration is stopped and the resin at the contact surfaces is cooled and solidified, thereby bonding the resin parts.
However, according to the conventional technique described above, when variations occur in the state of heating of the contact surfaces during the vibrating operation because of variations in the pressing force, the state or degree of melting of the resin at the contact surfaces varies. When the degree or state of melting of the resin at the contact surfaces varies, there is a problem that when the resin is cooled and solidified, a stable bonding state can not be obtained.
The present invention has been made in view of the problem of the conventional technology. It is an object of at least one embodiment of the present invention to provide a method for vibrating, melting and bonding resin parts capable of producing a bonded part in which the resin parts are stably bonded to each other.
In order to achieve the object described above, an aspect according to one embodiment of the invention is characterized, in FIG. 1, in that in a method for vibrating, melting and bonding at least two resin parts (7, 8) by making the at least two resin parts (7, 8) abut against each other and vibrating their contact surfaces (71 and 82 of FIG. 2) while applying a pressing force to them, the pressing force is sharply increased to a predetermined value P1 and then is gradually increased.
According to an embodiment of the invention, after a heating operation is started, the pressing force is increased sharply to the predetermined value P1 to facilitate heat generation. However, if the same pressing force is applied continuously to the contact surfaces (71, 82) of the resin parts (7, 8) after they are heated, the resin material at the contact surfaces (71, 82) is excessively heated and becomes degraded. For this reason, according to an embodiment of the present invention, after the pressing force reaches the predetermined value P1, the pressing force is gradually increased to push out the heated resin material from the contact surfaces (71, 82). This exposes a new surface of the resin material which is not heated so much and thus prevents the resin material at the contact surfaces (71, 82) from being excessively heated.
In this connection, since the contact surfaces (71, 82) of the resin parts (7, 8) are not completely flat, variations occur in heating the contact surfaces (71, 82) of the resin parts (7, 8). In order to obtain consistent melting and bonding throughout the contact surfaces (71, 82), it is necessary to apply heat as uniformly as possible throughout the contact surfaces (71, 82). Therefore, it is necessary to melt the resin material at the contact surfaces (71, 82) in a uniform manner to achieve consistency in heating the contact surfaces (71, 82). In this case, even if variations occur in heating the contact surfaces (71, 82) of the resin parts (7, 8), it is possible to prevent parts of the resin material from being excessively heated.
In this manner, by preventing the resin material at the contact surfaces (71, 82) of the resin parts (7, 8) from being excessively heated, it is possible to solidify the resin material which does not deteriorate and is nearly uniform in the state of melting throughout the contact surfaces (71, 82) to produce a well-bonded part. Additionally, the pressing force is continuously and gradually increased until the vibrating of the contact surfaces is finished. This makes it possible to prevent the resin material from being excessively heated by the heat generated by the vibrating operation.
In another aspect, the pressing force is continuously gradually increased from the predetermined value P1 in a range not exceeding a predetermined upper limit pressing force P2. If the pressing force exceeds the predetermined upper limit pressing force P2, the resin material is removed from the contact surfaces before the resin material is sufficiently heated and thus there is the possibility that acceptable bonding can not be achieved. For this reason, it is effective to increase the pressing force gradually in the range so as not to exceed the predetermined upper limit pressing force P2. Alternatively, the pressing force may be continuously gradually increased by a combination of a period in which the pressing force is held at a constant value and a period in which the pressing force is increased. In order to increase the pressing force gradually, of course, the pressing force may be increased continuously (linearly), and an increasing gradient of the pressing force may be increased gradually as a whole by combining the period in which the pressing force is held at a constant value with the period in which the pressing force is increased.
With respect to vibration, after the vibrating of the contact surfaces is started, a moving speed of the contact surfaces (71, 82) may be sharply increased to a predetermined upper limit and the moving speed may thereafter be decreased gradually. According to an embodiment of the invention, after the vibrating operation is started, by sharply increasing the moving speed to the predetermined upper limit, heating is facilitated to melt the resin material at the contact surfaces (71, 82). By decreasing the moving speed gradually after the resin material at the contact surfaces (71, 82) of the resin parts (7, 8) is heated and melted, heat generation is decreased to prevent the resin material at the contact surfaces from being excessively heated, which may promote material degradation. Therefore, it is possible to solidify the resin material which is not yet degraded and in a state of melting to obtain a well-bonded part.
Continuing with an embodiment of the preset invention, the position of one 8 of the two resin parts (7, 8) is measured as the amount of melting M of the resin parts (7, 8) at the contact surfaces (71, 82) with reference to the other resin part 7, is in progress. A determination is made whether the amount of melting M increases with the lapse of time or not; and on the basis of the determination result, a determination is made whether the melting and bonding of the resin parts (7, 8) is acceptable.
In the related art, when the amount of melting at the contact surfaces of the resin parts reaches a predetermined amount, the vibrating operation is stopped and the melting resin material at the contact surfaces is solidified to complete the bonding of the contact surfaces. In the case where variations occur in the state of melting of the resin material at the contact surfaces because of variations in heating when the vibrating operation is carried out, the amount of melting hardly increases (or may only increase a little) until the resin material at the portion where heat generation does not yet progress is sufficiently heated and melted. Then, when the whole contact surface is melted, the amount of melting increases at a portion and reaches a predetermined amount, but the resin material at the portion where the heat generation progresses from the start is excessively heated and becomes degraded.
For this reason, in an embodiment of the present invention, a determination is made whether the amount of melting M increases with the lapse of time, and in the case where the amount of melting M is increased with the lapse of time, it is possible to determine that the resin material being excessively heated and degraded is not at the contact surfaces. Therefore, it is possible to determine, on the basis of the result of determination on whether the amount of melting M increases with the elapse of time or not, whether the melting and bonding is good or not. In this manner, it is possible to obtain the bonded part in which the resin parts (7, 8) are well bonded.
The result of the determination on whether the amount of melting M increases with the lapse of time or not can be obtained by determining whether or not the amount of melting M is within a range from an upper limit to a lower limit (U, J) both of which increase with the lapse of time, or by determining whether or not the target amount of melting is obtained within the predetermined time.
Further, in another aspect, one resin part 7 of at least two resin parts (7, 8) has a projection 72 on its outer peripheral surface. The resin part 7 is pressed into the holding portion 6a of a vibrating jig 6 to fix the vibrating jig 6. The vibrating jig 6 is vibrated in this state to vibrate the contact surfaces (71, 82).
In the related art, in a general method for vibrating, melting and bonding resin parts, a small clearance is made between a holding portion of the vibrating jig and the outer peripheral surface of the resin part mounted on the vibrating jig. This clearance causes a loss of energy in transmission while the vibrating operation is performed and a variation in clearance produces a variation in vibration energy transmitted to the contact surfaces of the resin parts.
In an embodiment of the present invention, since the resin part 7 has the projection 72 on its outer peripheral surface and the resin part 7 is pressed into the holding portion 6a of a vibrating jig 6 to fix the vibrating jig 6, the vibration energy can be accurately transmitted. Therefore, the present invention hardly produces a variation in the vibration energy transmitted to the contact surface 71 of the resin part 7 and can produce a bonded part in which the resin parts (7, 8) are well-bonded.
Further, one resin part 7 may be fixed to the vibrating jig 6 and another resin part 108 maybe fixed to a stationary jig 13, the vibrating jig 6 is vibrated to vibrate the contact surfaces (71, 82). The stationary jig 13 has receiving surfaces (114, 115) in accordance with the shape of the other resin part 108 and causes a uniform pressing force to be applied to the contact surfaces (71, 82) when the contact surfaces (71, 82) are vibrated.
According to this embodiment of the invention, even if the resin part 108 fixed to the stationary jig 13 is formed in a complex shape, it is possible to make the pressing force applied to the contact surfaces (71, 82) uniform when the contact surfaces (71, 82) are vibrated. Therefore, there is hardly a variation in the state of heating of the resin material at the contact surfaces (71, 82). In this manner, it is possible to produce a well-bonded part with the resin parts (7, 108). Further, the receiving surfaces (114, 115) of the stationary jig 13 are provided with a movable part 115, and the movable part 115 can move according to the shape of the other resin part 108, and when the contact surfaces (71, 82) are vibrated, the movable part 115 can be fixed to cause a uniform pressing force against the contact surfaces (71, 82).
Further, contact surface 82 is formed so as to make the rigidity of the resin part nearly uniform at each portion of the contact surface 82. If the resin parts of the contact surfaces are different in rigidity between respective portions thereof, the portion having lower rigidity is vibrated in synchronization with the vibration, when they are vibrated, and thus does not generate heat as much as the portion having higher rigidity. In this manner, if the resin parts of the contact surfaces are different in rigidity between respective portions thereof, heat generation progresses in the portion having higher rigidity and results in non-uniform heating. Therefore, this results in varying the state of melting of the resin material at the contact surfaces and does not produce good bonding.
In an embodiment of the present invention, since the contact surface 82 is formed such that the rigidity of the contact surface 82 of the resin part is nearly uniform, variations are unlikely to occur in heating the resin material of the contact surface 82. Therefore, it is possible to produce a bonded part in which the resin parts are well-bonded to each other.
Further, when the contact surface 82 is formed in a polygonal shape, by making the thickness of the resin part of the corner 811 of the resin part thinner than that of the straight portion 812 of the resin part, the rigidity of the resin part can be made nearly uniform at each portion of the contact surface 82.
In a state where one resin part 7 is fixed to the vibrating jig 6 and the other resin part 8 is fixed to the stationary jig 13, the vibrating jig 6 is vibrated to vibrate the contact surfaces (71, 82), and the other resin part 8 has a polygonal rib portion 81 whose top surface is the contact surface 82, and the thickness W1 of the rib portion 81 at its corner portion 811 is made thinner than the thickness W2 of the rib portion 81 at a straight portion 812, thereby making the rigidity of the resin part nearly uniform at each portion of the contact surface 82. Still further, in another aspect, at least one resin part 208 has a step at the contact surface 282 and that a portion 912 having a higher rigidity of the resin part at the contact surface 282 is projected from a portion 911 having a lower rigidity of the resin part at the contact surface 282.
Accordingly, it is possible to make heat generation progress earlier at the portion 912 having lower rigidity of the resin parts of the contact surface 282. Therefore, it is possible to prevent uneven and inconsistent heating of the resin material at the contact surface 282 and thus to produce a bonded part in which the resin parts (7, 208) are well-bonded.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.